Sized paper comprising a polymerized alkylenimine



- corporation of acid-sensitive fillers.

United States Patent SIZED PAPER COMPRISING POLYMERIZED ALKYLENIMINE Chester G. Landes, New Canaan, and Walter F. Reynolds, Jr., Stamford, Conn., assignors to American Cyan- 1a/Imid Company, New York, N. Y., a corporation of ame No Drawing. Application April 11, 1952, Serial No. 281,918

15 Claims. (Cl. 92-21) This invention relates to the sizing of cellulosic fibers and to the formation of cellulosic felts therefrom of improved resistance to aqueous fluids. More particularly, the present invention relates to the synergistic combination of an alkaline sizing agent and an alkylenimine resin with cellulosic fibers in aqueous medium, and the formation of the thus-treated fibers into felts of improved ink and water resistance.

The manufacture of sized paper containing acid-sensitive fillers has long presented a definite problem to the art. The principal difiiculty arises from the fact that the alkaline fillers commonly used, for example calcium carbonate and Raffold (calcium carbonate-magnesium hydroxide) impart an excessively high pH to the paper pulp suspensions, on the order of 8.09.0, whereas the size, typically sodium rosinate, can be precipitated on the fibers only under acid conditions, for example, atpH values between 4-6. It. is not practical first to size the fibers under acid conditions and in a subsequent step to incorporate the carbonate filler under alkaline conditions, as under alkaline conditions the size is rapidly desorbed by the fibers resulting in the formation of paper of reduced water and ink resistance. The reverse procedure is equally impractical, as the carbonate is in substantial part destroyed by the acid, with formation of foam and bubbles, resulting in the formation of a non-homogeneous paper.

Recently, a group of cationic, hydrophobic, organic compounds has been discovered which eliminates these difficulties. These compounds are substantive to cellulose fibers in aqueous suspension, and possess the valuable property of maintaining their substantivity under the alkaline conditions required for the most effective in- The compounds are characterized by a cationic, hydrophilic basic nitrogenous group and by at least one long chain hydrophobic aliphatic radical containing 14-22 carbon atoms, the long chain aliphatic radical being attached to the basic nitrogenous group.

The present invention is based on the discovery that the self-polymers ethylenimine,

CHr-CH:

and of alkylenimines containing not more than four carbon atoms, in their water-soluble, hydrophilic stage, act synergistically with the above-described sizingagents. It has been found that when a small proportion of the alkylenimine resin is absorbed by a stock of cellulosic fibers in aqueous suspension, either before or after the sizing agent has been added, and the fibers bearing both the alkylenimine resin and the sizing agent are sheeted and dried at an elevated temperature to develop the water repellant properties of the size, a paper is obtained which has a greater ink and water resistance than 18 afforded by the total water and ink resistance imparted by either the alkylenimine resin or the sizing agent employed separately. The cause of this surprising result 15 not known, and applicants do not wish to be .bound by any pa'rticular theory.

ice

The cellulosic sheets produced according to the process of the present invention find particular use for applications where high wet strength coupled with high water irnpermeability are desired. Such applications include paper bags, wrapping paper, and laminating paper for the formation of cardboard and paper board useful in the manufacture of paper containers.

It is a most beneficial feature of the present invention that, so far as is known, the synergistic action of the alkylenimine resin is not accompanied by any harmful effect, so that all benefits afforded the use of the sizing agents and the alkylenimine resins taken singly are retained when the two classes of materials are used in combination. Still another advantage is that no subsequent treatment of the fibers is necessary, other than those inherently required to develop the sizing properties of the sizes used. A most important advantage of the present invention is that it makes it possible to reduce the consumption of sizing agents of the class described to a fraction of that previously thought necessary to produce a sized paper of acceptable ink and water resistance.

It is a further important advantage of the alkylenimine resins that their use does not require any adjustment in the manner in which such materials as starch, gum, wax sizes, and other organic sizing or filling agents have been previously incorporated with the fibers. We have found that from 0.1-3% or more of these additional sizing and filling agents, based on the dry weight of the paper pulp, added after the incorporation of the alkaline sizing agent and the alkylenimine resin, results in still further improvement of the finished paperin water resistance and in ink resistance. Suitable starches are cornstarch, preferably cooked, potato starch, wheat starch, soya bean starch and the like. Locust bean gum, starch, and other mannogalactans may be employed, as well as casein and other proteins, preferably solubilized with borax or other alkali. In addition, any of the commercially available wax size emulsions may be employed.

It is an additional advantage of the use of alkylenimine resins that the water-laid sheets develop a very pronounced tackiness while they are drying. As a result, it is possible to laminate a sheet of paper produced according to the process of the present invention with an unsized sheet of paper or paper board to yield a composite paper or paper board having an adsorbent body but possessing great surface water and ink resistance. Thus a laminated blotting paper may be produced having an ink-resistant surface. It is further possible to make a well laminated cardboard of improved ply-strength by the use of this intrinsic adhesiveness.

Briefly, according to the process of the present invention, small amounts of an aqueous solution or dispersion of the alkylenimine resin and an aqueous solution or dispersion of the sizing agent are separately added to a stock of cellulosic fibers at any ordinary consistency in the beater. The order in which these materials is not critical, but before each addition the pH of the stock is adjusted to suitable values as discussed below, and after each addition the stock is aged until the added material has been adsorbed by the fibers. The resulting stock is sheeted and dried in the normal fashion, and then is subjected to sufficient heating to develop the water-repellent properties of the size.

The alkylenimine resin is strongly bound to the fibers, apparently by electrostatic forces, and cannot be leached therefrom by water. So far as is known the resin does not react or undergo further polymerization while on the fibers. The paper in its simplest embodiment thus consists essentially of cellulosic fibers, the size and the resin, both the size and the resin being uniformly distributed throughout the sheet and firmly adsorbed by the fibers.

The synergistic action described above occurs to a significant degree with all commercial pulps, so that the character of the stock is not critical in the present invention. Good results have been obtained with bleached and 3 unbleached northern kraft pulps and with a stock made fromcorrugated boxboard containing a high percentage ofsodium silicate.

In the adding the agents described, it is advantageous to maintain the pH of the pulp within the ranges at which the sizing agent and the alkylenimine resin are respectively best adsorbed. in this respect, the sizing agents exhibit a variable behavior. All so far investigated are adsorbed very well on the acid side, for example, in the pH range of about 4 to 6. Some, however, are adsorbed on the alkaline side as well, that is, at pH values as high as 10. In the majority of cases, then, the sizing agent is added first with the stock at a pH of about 4-6. The alkylenimine resin is added after the pH of the stock has been ad usted to a value between 8 and a pH insufficiently high to harm the fibers. A pH of 11 gives good results without harming the stock.

The alkaline sizing agents and alkylamine resins mentioned above are mutual precipitants and therefore the addition of each should be sequential and not simultaneous. Moreover, while the absorption of both classes of materials by the fibers is very rapid when the stock is maintained at respectively suitable pH values, some shortperiod of aging is required before absorption in each instance becomes substantially complete. Ordinarily an aging period of about five minutes is ample, and a shorter time will frequently be found sufficient.

The synergistic action set forth above is very evident when as little as of alkylenimine resin is added based on the weight of sizing agent, so that there does not appear to be any lower limit to the amount of alkylenimine resin which will produce at least some synergistic action. Maximum synergistic action appears to take place in most instances when the amount of alkylenimine resin added is between about 1 and 3 times the weight of sizingv agent. As ordinarily between about /2% and 5% of sizing agent is added, based on the weight of the fibers, the amount of alkylenimine resin added will generally'be at least about /2% of the weight of the fibers. It will be evident that much larger amounts of the alkylenimine resin may and frequently will be added to the stock above that necessary to produce the maximum synergistic effect. Such additional amounts, which may be as high as 400% of the weight of the sizing agent or higher, are within the scope of the invention.

The' alkylenimine resins suitable for use in the process of the present invention are prepared by carefully heating monomeric ethylenimine, propylenimine, or butylen'imine, or mixtures thereof in the presence of a catalyst, until polymerization has proceeded sufliciently far to form a resin which is hydrophilic and cationic but insuificiently far to render the resin hydrophobic. The end point may readily be found by testing the resin for these properties against paper pulp vor by determining the viscosity of the' resin as the self-condensation proceeds. A suitable resin has a viscosity of 60-120 seconds, measured by the fall time of a 3 mm. steel ball throughZO mm. of a 50% aqueous solution of the polymer at C..

It is a most important feature of the invention that theme of the alkylenimine resins does not preclude the incorporation of acid-sensitive fillers, colorants and assistants. To incorporate these materials it isonly necessary, of course,.that the pH of the stock is not acid at the time'of additionand is not made acid at a point subsequent thereto. Thus, Where the sizing agent and the alkylenimine resin are both added with the pulp on the acid side, the stock shouldbe made distinctly alkaline before the acid-sensitive fillers are incorporated. On the other hand, where the sizing agent is added on the acid side, and the alkylenimine resin is added on the alkaline side, as is preferred, the fillers and colorants may be added immediately before, with, or subsequent to the incorporation of the resin.

The sizing agents are advantageously prepared from fatty amines or acids of between l4-22 carbon atom chain length. The fatty radicals may be saturated or unsaturated, but preferably will contain not more than about 50% of unsaturated molecules. In the case of fatty amines an efficient size is produced by first adding to the amine one mol of concentrated hydrochloric acid and sufiicient ethanol to form a solution. then adding two mols of epichlorohvdrin dropwise at 70 C., refluxing for 4 hours, and stripping off the solvent. A small amount. of acetic acid'may then be added to facilitate the dispersion of the product in water. Sizes are also prepared from the fatty acid by partial acylation of a polyalkylenepolyamine. I In this reaction the fatty acid and amine are mixed and heated at about 200 C. until evolution of water substantially ceases, the amount of fatty acid taken being insufiicient to react with all the primary and secondary groups in the amine. An excellent product is obtained by reacting 3 mols of stearic acid with 1 mol of tetraethylenepentamine. The product is made dispersible by reaction of acid with the unreacted amine groups or by reaction of the free amine groups with one to two molsof-epichlorohydrin. In this step the partially acylated polyalkylenepolyamine issuspended in an equal .volume of ethanol, one to' two mols of epichlorohydrin added, themixturerefiuxed for 4 hours, and the solventstripped ofli.

Thechemical formulae of these'compounds. is' not known, and therefore the compoundsare referred to hereinafter in terms of their method of fo'rmatiom.

The invention will be further described by the following specific examples. Although .these examples describe certain features of the invention :indetail, the invention has been fully set forth above and the examples are given only for purposes-of-illustration and the invention is not limited thereto. Parts are by weight except where otherwise stated.

Examples 1-8 A slush stock was-prepared from'used corrugated-boxboard by pulping-the boxboard, passing the pulp through a refiner, and jordaning -,the slurry toabout: 600 :cc.

Schoepper-Riegler freeness. The pHwof the :resulting stock was adjusted vto :10.0 with l aqueous sodium: hydroxide. The stockwas then refined ina Morden refiner for 3 minutes, and two portions withdrawn at 2.0%v fiber consistency. ThepH' of one of these portions:

was reduced to 5 by the additionof hydrochloric acid.-

Five aliquots were withdrawn from each.of these 'two portions and one aliquot from'each set was labelled=as the controL.

The pulps of. the two control samples were'zsheeted, dried, and heated at C. for 2 minutes under'identical conditions,.and the resulting handsheetstestedfor their.

allowed to-age S minutes, J when absorption of...'the'..re-: agentsrwas substantially.complete All the 'pulps were: than diluted to .0.6% consistency, their 'pI-I adjusted to. 10.0, and made into lNa'shhandshee'tsiat a 'basis weight (25 x 40/5'00) of 47:4 pounds after a further agingperiod of five minutes. The percentage of ethylenimine resin. in the dried .paperhandsheets-producedTby Ex-a amples 3, 4, 5, 8,9 and IO-Was' determined 'bynitrogen analysis, allowance being'made' for the nitrogen content of both the control sample and the alkaline-size presenti The percentage of polyethylenimine in these-- sheets was guasstj mtially constant in thehighlrange of 2.45% to The tensile strength of the handsheets after aging for two weeks at 70 F. at 50% relative humidity were taken longitudinally and transversely and the results averaged. The water and-ink resistance ofthe' sheets were determined-by the-Currier and'B. K. Y. methods respectively, by applying the liquids to the felt sideof -the'- sheet and noting the number of seconds required for the liquids to pass through. In the case of' wate'rythe end point was determined by anautomatic electrical instrument operating by conductivity 'whieh recorded-the-time in seconds between-the instant-"at whichthe sheets were wetted with-a predetermined amount of water; and the instant at'whichthe'wate'r penetrated." In the'case-of' the ink, the end-point was determined by an automatic instrument employing a photoelectric cell, which recorded the time in-seconds' between the 'instant at'which' the ink'was added'to 'oneside of-the'paper, and-the instant at' which the dark 'blue' colorofth'e inkappea'r'ed on the other side. In the case of the controlsKEitample's 1 and 6), both the water and the ink passed through the paper practically instantaneously.

INITIAL PH OF STOCKPH 5.0

Order of addition Resistance (seconds), ig g Currier 1b Expt. First Second B. K. Y.

Size b Resin b Size b Resin b Water Ink Dry Wet Percent Percent Percent Percent 1 17.0 1.0 2 1.5 11 60 14.0 1.0 3 3 i 2 40 19.0 5.6 4 3 1.5 55 1,060 17.4 6.6 5 1.5 3 45 770 17.4 7.2

STOCK AT PH 10.0 THROUGHOUT 6 17.0 0.8 7 1.5 10 60 14.6 0.8 a 3 2 45 18.8 5.4 9 3 1.5 61 1,055 16.8 6.6 in 1.5 3 69 1,320 16.2 6.6

9 pH raised to 10.0 immediately prior to the addition of the ethyleni mine resin.

b Based on the dry weight of the fibers.

Instantaneous.

This table shows that when only the alkaline size was added to the stock, the water resistance of the paper increased to 11 seconds, and that when only polyethylenimine was added, the water resistance increased by 2 seconds. When however, the two materials were present on the fibers in combination, the water resistance increased to 45 seconds when the alkaline size was added first and the alkylenimine resin added second with the stock at a pH of 5.0. A maximum resistance of 69 seconds was obtained when the same order of addition was followed with the stock maintained at a pH of 10.0 throughout. An even more striking increase was efiected in the case of ink resistance, as the cumulative effect of the two materials employed separately was only about 100 seconds, whereas, when the two materials were employed together, the ink resistance increased to about 770 seconds in the case of experiment 5, and to 1320 seconds in the case of experiment 10.

Example 9 A size was prepared by condensing 63 parts of tetraethylenepentamine with 199 parts of a mixture of 16-18 carbon atom fatty acids obtained by the hydrogenation of tallow at 200 C. until evolution of water had substantially ceased, and solubilizing the product with one mol of glacial acetic acid. A stock of bleached kraft pulp at 0.6% consistency was prepared, and divided into several aliquots. One aliquot was retained as'control. To the second aliquot was added 1 /2% of the size described with the stock at pH 5.0. To the third aliquot was added 3% of cationic hydrophilic ethylenimine resin at pH 10.0. To the fourth aliquot was added first 1V2% of the size followed, after 5 minutes of aging, by 3% of cationic, hydrophilic ethylenirnine resin with the stock at pH 10.0. The pH adjustments were made by the use of aqueous sodium hydroxide, the size and the resin were added as 10% aqueous solutions or dispersions, and in each instance the stocks were allowed to stand until adsorption of the size and resin had become substantially complete. Handshects were prepared from each of the four aliquots as described above and heated for 2 minutes at 115 C. to develop the water-repellent properties of the size. The sheets were conditioned at 70 F. and 50% relative humidity for two weeks and tested for their resistance to penetration by water by the Currier method. Results are as follows.

Size Resin Water readded, added, sistance, percent percent seconds 1 Instantaneous.

We claim: 1

1. In a process for producing a sized cellulosic sheet of improved water and ink resistance, wherein '/z% to 5%, based on the weight of the fibers, of a cationic, organic, water-insoluble hydrophobic sizing agent in the form of a water-dispersible salt thereof is added to a stock of cellulosic fibers in aqueous suspension, said stock is allowed to stand until adsorption of said resin is substantially complete, said fibers are formed in a sheet, and said sheet is dried and heated at a temperature between about C. and C. for /2 to 3 minutes to develop the sizing properties of said sizing agent, the steps of separately adding to said fibers in said medium an aqueous solution of an alkylenimine resin in its hydrophilic, cationic stage, said resin being formed by polymerization of an alkylenimine containing not more than 4 carbon atoms, the weight of said alkylenimine resin being about M to 4 times the weight of said alkaline sizing agent, and allowing the stock to stand until adsorption of said resin is substantially complete.

2. In a process for producing a sized cellulosic sheet of improved water and ink resistance, wherein /z% to 5%, based on the weight of the fibers, of a cationic, organic, water-insoluble hydrophobic sizing agent in the form of a water-dispersible salt thereof is added to a stock of cellulosic fibers in aqueous suspension, said sizing agent being selected from the group consisting of the reaction product of a fatty amine with 1 to 2 mols of epichlorohydrin, the product formed by reacting sufficient of a fatty acid with a polyalkylenepolyamine to yield a water-insoluble amide but insufiicient to acylate all of the primary and secondary nitrogen atoms in said polyalkylenepolyamine, and the reaction product thereof with 1 to 2 mols of epichlorohydrin, said stock is allowed to stand until adsorption of said resin is substantially complete, said fibers are formed in a sheet and said sheet is dried and heated at a temperature between about 105 C. and 150 C. for /2 to 3 minutes to develop the sizing properties of said sizing agent, the steps of separately adding to said fibers in said medium an aqueous solution of an alkylenimine resin in its hydrophilic, cationic stage, said resin being formed by polymerization of an alkylenimine containing not more than 4 carbon atoms, the weight of said alkylenimine resin being about ,6 to 4 times the weight of said alkaline sizing agent, and allowing the stock to stland until adsorption of said resin is substantially comp ete.

3. A process according to claim 2 wherein the resin is polymerized ethylenimine.

4. A process according to claim 2 wherein the sizing agent is the reaction product of a fatty amine with 1 to 2 mols of epichlorohydrin.

5. A process according to claim 2, wherein the sizing agent is the product formed by reacting sufiicient of a fatty acid with a polyalkylenepolyamine to yield a waterinsoluble amide but insuificient to acylate all of the primary and secondary nitrogen atoms in said polyalkyl= enepolyamine.

6. A process according to claim 2 wherein the sizing agent is the product formed by reacting sufiicient of a fatty acid with a polyalkylenepolyamine to yield a waterinsoluble amide but insuflicient to acylate all of the primary and secondary nitrogen atoms in said polyalkylenepolyamine, and reacting the product with 1 to 2 mols of epichlorohydrin.

7. A process according to claim 2 wherein the size is added first with the stock at a pH of 4 to 6 and the resin is added subsequently when adsorptioii of the size is complete with the stock at a pH of 8 to 11.

8. As a new and useful composition of matter, a sheet of cellulosic fibers having uniformly adsorbed thereon between /z% and 5% of their weight of a cationic, organic, hydrophobic size, and 10% to 400% of an alkylenimine resin based on the weight of the size said sheet having been made by the process of claim 9.

9. As a new and useful composition of matter, a sheet of cellulosic fibers having uniformly adsorbed thereon between /2% and 5% of their weight of a cationic, organic, hydrophobic size selected from the group consisting of the reaction product of a fatty amine with 1 to 2 mols of epichlorohydrin, the product formed by reacting sufficient of a fatty acid with a polyalkylenepolyamine to yield a water-insoluble amide but insuificient to acylate all of the primary and secondary nitrogen atoms in said polyalkylenepolyamine-'andthe"reaction product thereof with-1 to. 2 mols of epichlorohydrin;- and" 10% to 400% of an alkylenimine-resin' the reaction product of a fatty amine with 1 to 2 mols of epichlorohydrin.

13. A sheetaccording to' claim 9whereinthe size is-.1he-'product formed by reacting suflicient of a fatty acid-with a polyalkylenepolyarnine to yield a waterinsoluble-amide but insuflicientto acylate all of the primary and. secondary nitrogen atoms-in said polyalkylenepolyarnine.

14."-A sheet according 'to"claim=9 wherein'the' size-is: the product formed by-reacting sufiicient'of a fatty acid with a polyalkylenepolyarnine.to yield a water-insoluble amide but insuflicient toflacylate all of'the. primary and.

secondary nitrogenatoms in said polyalkylenepolyamine, and reacting the product with 1 to 2 'mols of epichlorohydrin.-

15.As a new and useful composition-of matter, a laminate comprising at least one sheet corresponding to 10 that ofclaim 8.

References Cited in thefileof this patent UNITED STATES PATENTS 15 2,269,997 Berchet; Jan. 13, 1942 2,444,802 Auten July 6, 1948' 2,479,480 Dudley Aug.- 16, 1949 

1. IN A PROCESS FOR PRODUCING A SIZED CELLULOSIC SHEET OF IMPROVED WATER AND INK RESISTANCE, WHEREIN 1/2% TO 5%, BASED ON THE WEIGHT OF THE FIBERS, OF A CATIONIC, ORGANIC, WATER-SOLUBLE HYDROPHOBIC SIZING AGENT IN THE FORM OF A WATER-DISPERSIBLE SALT THEREOF IS ADDED TO A STOCK OF CELLULOSIC FIBERS IN AQUEOUS SUSPENSION, SAID STOCK IS ALLOWED TO STAND UNTIL ADSORPTION OF SAID RESIN IS SUBSTANTIALLY COMPLETE, SAID FIBERS ARE FORMED IN A SHEET, AND SAID SHEET IS DRIED AND HEATED AT A TEMPERATURE BETWEEN ABOUT 105* C. AND 150* C. FOR 1/2 TO 3 MINUTES TO DEVELOP THE SIZING PROPERTIES OF SAID SIZING AGENT, THE STEPS OF SEPARATELY ADDING TO SAID FIBERS IN SAID MEDIUM AN AQUEOUS SOLUTION OF AN ALKYLENIMINE RESIN IN ITS HYDROPHILIC, CATIONIC STAGE, SAID RESIN BEING FORMED BY POLYMERIZATION OF AN ALKYLENIMINE CONTAINING NOT MORE THAN 4 CARBON ATOMS, THE WEIGHT OF SAID ALKYLENIMINE RESIN BEING ABOUT 1/10 TO 4 TIMES THE WEIGHT OF SAID ALKALINE SIZING AGENT, AND ALLOWING THE STOCK TO STAND UNTIL ADSORPTION OF SAID RESIN IS SUBSTANTIALLY COMPLETE. 